Clock integrated circuit

ABSTRACT

The clock circuit of an integrated circuit operates with variations such as temperature, ground noise, and power noise. Various aspects of an improved clock integrated circuit address one or more of the variations in temperature, ground noise, and power noise.

BACKGROUND

1. Field of the Invention

The present technology relates to an integrated circuit with a clockcircuit, tolerant to variations such as temperature, ground noise, andpower noise.

2. Description of Related Art

The clock circuit of an integrated circuit operates with variations suchas temperature, ground noise, and power noise. Because these variationsaffect the final timing of the output clock signal, various approachesaddress the variations in order to generate a uniform output clocksignal despite the variations.

For example, U.S. Pat. No. 7,142,005 by Gaboury seeks to decouple powerfluctuations from the clock signal, by adding buffer circuits withactive loads, independent bias circuitry, and bias circuitry. Theserelatively complicated buffer circuits devote significantly more diearea, and cost, to isolating such power fluctuations from the clockcircuit.

What is needed is an approach to address such variations with reducedcomplexity and cost.

SUMMARY

One aspect of the technology is an apparatus with a clock integratedcircuit.

The clock integrated circuit has a timing circuit with an outputalternating between a first reference signal and a second referencesignal at a rate determined by a time constant determining timing of aclock signal output of the clock integrated circuit. The secondreference signal includes a varying noise signal, such as varying powernoise.

The clock integrated circuit also has clock power and referencecircuitry, which has the varying noise signal. The clock power andreference circuitry generates the second reference signal with a firstversion of the varying noise signal. The clock power and referencecircuitry also generates a level switching reference signal with asecond version of the varying noise signal. The first version of thevarying noise signal is synchronized with the second version of thevarying noise signal, such that variations in the first version of thevarying noise signal are synchronized with variations in the secondversion of the varying noise signal.

The clock integrated circuit also has a level switching circuitcomparing an output of the timing circuit with the level switchingcircuit reference signal. An output of the level switching circuitdetermines the clock signal output of the clock integrated circuit.

In one embodiment, the variations in the first version of the varyingnoise signal have different magnitudes from the variations in the secondversion of the varying noise signal.

In one embodiment, the clock power and reference circuitry has a firstoutput for the second reference signal, and a second output for thelevel switching reference signal, and the varying noise signal issynchronized across the first output and the second output via aresistance coupled between the first output and the second output. Inone embodiment, the varying noise signal is synchronized across thefirst output and the second output via a capacitance coupled between thefirst output and the second output. In one embodiment, one of the firstoutput and the second output is floating for this capacitive coupling.

One embodiment further includes switches decoupling the level switchingcircuit during power on.

In one embodiment, the first reference signal is a first referencevoltage, the second reference signal is a second reference voltage, andthe timing circuit alternates between charging from the first referencevoltage to the second reference voltage and discharging from the secondreference voltage to the first reference voltage.

In one embodiment, the time constant characterizes an exponentialsignal.

In one embodiment, the clock integrated circuit further includes a latchcircuit generating the clock signal output of the clock integratedcircuit, responsive to the output of the level switching circuit.

Some embodiments include a level switching reference circuit generatingthe level switching reference signal. The level switching referencecircuit includes an output generating the level switching referencesignal. In various embodiments the level switching reference circuitincludes a PTAT current generator or CTAT current generator, thatgenerates current flowing by the output. In various embodiments thelevel switching reference circuit includes a resistance adjacent to theoutput or a parallel resistance and capacitance adjacent to the output.

One aspect of the technology is a clocking method. Some embodimentsinclude the steps of:

determining timing of a clock integrated circuit by alternating a timingcircuit output between a first reference signal and a second referencesignal at a rate determined by a time constant determining the timing ofthe clock integrated circuit;

generating the second reference signal with a first version of a varyingnoise signal and a level switching reference signal with a secondversion of the varying noise signal, the first version of the varyingnoise signal synchronized with the second version of the varying noisesignal, such that variations in the first version of the varying noisesignal are synchronized with variations in the second version of thevarying noise signal; and

comparing the timing circuit output with the level switching referencesignal, to determine a clock signal output of the clock integratedcircuit.

In some embodiments, the varying noise signal is a varying power noise.

In some embodiments, the variations in the first version of the varyingnoise signal have different magnitudes from the variations in the secondversion of the varying noise signal.

In some embodiments, said generating includes:

synchronizing the first version and the second version of the varyingnoise signal by coupling the second reference signal and the levelswitching reference signal with a resistance.

In some embodiments, said generating includes:

synchronizing the first version and the second version of the varyingnoise signal by coupling the second reference signal and the levelswitching reference signal with a capacitance.

In some embodiments, said generating includes:

synchronizing the first version and the second version of the varyingnoise signal by floating one of the second reference signal and thelevel switching reference signal, and coupling the second referencesignal and the level switching reference signal with a capacitance.

Some embodiments further include:

decoupling the synchronized versions of the varying noise signal duringpower on, such that said determining and said comparing do not rely onthe synchronized versions of the varying noise signal during power on.

In some embodiments, the first reference signal is a first referencevoltage, the second reference signal is a second reference voltage, andthe timing circuit alternates between charging from the first referencevoltage to the second reference voltage and discharging from the secondreference voltage to the first reference voltage.

In some embodiments, the time constant characterizes an exponentialsignal.

Some embodiments further include:

after said comparing, generating the clock signal output of the clockintegrated circuit with a latch circuit.

One aspect of the technology is a method of manufacturing an apparatus,comprising:

providing a clock integrated circuit, comprising:

providing a timing circuit having an output alternating between a firstreference signal and a second reference signal at a rate determined by atime constant determining timing of a clock signal output of the clockintegrated circuit, the second reference signal including a varyingnoise signal;

providing clock power and reference circuitry having the varying noisesignal, the clock power and reference circuitry generating the secondreference signal with a first version of the varying noise signal, theclock power and reference circuitry generating a level switchingreference signal with a second version of the varying noise signal, thefirst version of the varying noise signal synchronized with the secondversion of the varying noise signal, such that variations in the firstversion of the varying noise signal are synchronized with variations inthe second version of the varying noise signal; and

providing a level switching circuit comparing an output of the timingcircuit with the level switching circuit reference signal, an output ofthe level switching circuit determining the clock signal output of theclock integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an integrated clock circuit with toleranceto variations such as temperature, ground voltage, and power voltage.

FIGS. 2A and 2B are circuit diagrams of an integrated clock circuit withtolerance to temperature variations, including inverter circuitry toevaluate the timing circuitry output, where FIG. 2A has capacitivetiming circuitry coupled towards the ground, and FIG. 2B has capacitivetiming circuitry coupled towards power.

FIG. 2C is a circuit diagram of an integrated clock circuit withtolerance to temperature variations, similar to FIG. 2A, but receivingpower from PTAT power sources rather than CTAT power sources.

FIG. 2D is a circuit diagram of an integrated clock circuit withtolerance to temperature variations, including Schmitt trigger circuitryto perform level detection of the timing circuitry output.

FIG. 2E is a circuit diagram of a Schmitt trigger, such as in FIG. 2D.

FIGS. 3A and 3B are circuit diagrams of an integrated clock circuit withtolerance to temperature variations, including op amp circuitry toperform level detection of the timing circuitry output, where FIG. 3Ahas capacitive timing circuitry coupled towards the ground, and FIG. 3Bhas capacitive timing circuitry coupled towards power.

FIG. 4A is a circuit diagram of the circuit for the reference signal forthe level detection circuitry including a PTAT current source, withoutput that decreases with increasing temperature

FIG. 4B is a circuit diagram of the circuit for the reference signal forthe level detection circuitry including a CTAT current source, withoutput that increases with increasing temperature.

FIG. 4C is a circuit diagram of the circuit for the reference signal forthe level detection circuitry including a current source, with outputthat increases with increasing temperature, and further including acapacitor in parallel with a load resistor of a current mirror.

FIG. 4D is a current generator based reference circuit providing PTATcurrent from PMOS devices.

FIG. 4E is a current generator based reference circuit providing PTATcurrent from NMOS devices.

FIG. 4F is a current generator based reference circuit providing CTATcurrent from PMOS devices.

FIG. 4G is a current generator based reference circuit providing CTATcurrent from NMOS devices.

FIG. 5A is circuit diagram of the circuit for the reference signal forthe level detection circuitry including a current source with currentoutput that decreases with increasing temperature, and an output thatdecreases with increasing temperature.

FIG. 5B is a circuit diagram of the circuit for the reference signal forthe level detection circuitry including a current source with currentoutput that increases with increasing temperature, with output thatincreases with increasing temperature.

FIG. 5C is a circuit diagram of the circuit for the reference signal forthe level detection circuitry including a current source with currentoutput that decreases with increasing temperature, with output thatincreases with increasing temperature.

FIG. 5D is a circuit diagram of the reference signal for the leveldetection circuitry as in FIG. 5C, but including a current source withcurrent output that increases with increasing temperature.

FIG. 5E is a variation of the circuit of FIG. 5C, where the constantcurrent source replaced with the resistor.

FIG. 6A is a set of graphs of time versus rising magnitude tracesshowing how clock circuitry that is intolerant of temperature variationgenerates clock timing that varies widely with varying temperature.

FIG. 6B is a set of graphs of time versus rising magnitude tracesshowing how clock circuitry that is tolerant of temperature variationgenerates clock timing is fairly constant with varying temperature, dueto circuitry such as that in FIGS. 2-5.

FIG. 7A is a set of graphs of time versus falling magnitude tracesshowing how clock circuitry that is intolerant of temperature variationgenerates clock timing that varies widely with varying temperature.

FIG. 7B is a set of graphs of time versus falling magnitude tracesshowing how clock circuitry that is tolerant of temperature variationgenerates clock timing is fairly constant with varying temperature, dueto circuitry such as that in FIGS. 2-5.

FIGS. 8A and 8B are circuit diagrams of an integrated clock circuit withtolerance to ground noise, including transistors that selectively couplethe ground noise as part of the reference signal used in level detectionof the timing circuitry output, where in FIG. 8A the switching referencecircuitry include capacitance circuitry coupled towards ground, and inFIG. 8B the switching reference circuitry includes capacitance circuitrycoupled towards power.

FIG. 9 is a set of graphs of voltage versus time, showing how clockcircuitry that is intolerant of ground noise, will generate clock timingthat varies widely with time-varying ground noise.

FIG. 10 is a set of graphs of voltage versus time, showing how clockcircuitry that is tolerant of ground noise, will generate clock timingthat is fairly constant with time-varying ground noise, due to circuitrysuch as that in FIG. 8.

FIGS. 11A and 11B are circuit diagrams of an integrated clock circuitwith tolerance to power noise, including transistors that share a commonnoise phase of power noise in the timing circuitry power, and powernoise in the reference signal used in level detection of the timingcircuitry output, where in FIG. 11A the capacitance circuitry is coupledtowards ground, and in FIG. 11B the capacitance circuitry is coupledtowards power.

FIG. 12 is a circuit diagram of the power circuitry that shares thecommon noise phase of power noise to in the timing circuitry power, andpower noise to in the reference signal used in level detection of thetiming circuitry output.

FIG. 13 is a set of graphs of voltage versus time, showing how powernoise has the same phase in both the timing circuitry power, and thereference signal used in level detection of the timing circuitry output,due to circuitry such as in FIGS. 11 and 12.

FIG. 14 is a set of graphs of voltage versus time, showing how clockcircuitry that is intolerant of power noise, will generate clock timingthat varies widely with time-varying power noise.

FIG. 15 is a set of graphs of voltage versus time, showing how clockcircuitry that is tolerant of power noise, will generate clock timingthat is fairly constant with time-varying power noise, due to circuitrysuch as that in FIGS. 11 and 12.

FIGS. 16A and 16B are circuit diagrams of an integrated clock circuitwith tolerance to power noise, including transistors that share a commonnoise phase of power noise in the timing circuitry power, and powernoise in the reference signal used in level detection of the timingcircuitry output, similar to FIG. 11, and adding switch circuitry toselectively bypass the noise tolerant circuitry, such as during poweron.

FIG. 17 is block diagram of a memory circuit with an improved integratedclock circuit as discussed herein.

FIG. 18 is a circuit diagram, similar to FIG. 16, of an integrated clockcircuit with tolerance to power noise, and further including switchingcircuitry between the reference generator and the op amp.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an integrated clock circuit with toleranceto variations such as temperature, ground voltage, and power voltage.

The clock integrated circuit generally has a loop structure, with timingcircuitry 102, level switching circuitry 104, and latch circuitry 106.The latch circuitry 106 generates a feedback signal from latch circuitry106 back to timing circuitry 102, and the clock signal output 110. Thetiming circuitry 102 alternates between two reference signals accordingto a time constant. The time constant accordingly determines the timingof the clock integrated circuit. A typical example of the time constantis an exponential time constant that characterizes the rise and fall ofan RC circuit or an RL circuit. The level switching circuitry monitorsthe output of the timing circuitry 102, and changes the output dependingon whether the timing circuitry 102 is sufficiently high, or low.Examples of latch circuitry 106 are an SR latch, SR NAND latch, JKlatch, gated SR latch, gated D latch, gated toggle latch. The latchcircuitry 106 has two stable states and alternates between the twostable states to generate the clock signal output 110.

The two reference signals relied on by the timing circuitry 102 aregenerated by circuitry 116, which also generates the level switchingreference relied on by the level switching circuitry 104. By commonlygenerating both the reference signals relied on by the timing circuitry102, and the level switching reference relied on by the level switchingcircuitry 104, circuitry 116 minimizes the noise phase of a noise signalshared by the reference signals relied on by the timing circuitry 102,and the level switching reference relied on by the level switchingcircuitry 104. Because any noise phase is minimal, peaks and valleys inthe noise signal that occur in the reference signals relied on by thetiming circuitry 102, are synchronous with peaks and valleys in thenoise signal that occur in the level switching reference relied on bythe level switching circuitry 104.

The level switching reference 112 relied on by the level switchingcircuitry 104, is selectively coupled to the level switching circuitry104 by circuitry 118. In some embodiments, this acts as a sample andhold of ground noise, so that the same ground noise is held by thetiming circuitry 102, and by the level switching reference circuitryrelied on by the level switching circuitry 104.

Although the shown block diagram addresses the variations intemperature, ground noise, and power noise, various embodiments of animproved clock integrated circuit address just one of these variations(e.g., just temperature, just power noise, or just ground noise), orjust two of these variations (e.g., just temperature and power noise,just temperature and ground noise, or just power noise and groundnoise).

FIGS. 2A and 2B are circuit diagrams of an integrated clock circuit withtolerance to temperature variations, including inverter circuitry toevaluate the timing circuitry output.

Shown are parallel instances of timing circuitry 202A and 202B, parallelinstances of inverter circuitry 204A and 204B, and the latch circuitry206. The timing circuitry 202A and 202B is generally an inverter withresistance RX or RY, charging to or discharging from capacitance CX orCY, to change the output voltage at OX or OY.

FIG. 2A shows an embodiment where the capacitance CX or CY is coupled toa common ground. Although all possible variations are not explicitlyshown in the Figures, the present technology covers all disclosedinstances of the clock circuit showing the capacitance CX or CY, wherethe clock circuit is modified to couple the capacitance CX or CY toground.

In one embodiment, the capacitance CX or CY is actually a PMOStransistor with the opposite terminal decoupled from a common groundwith the inverters.

FIG. 2B shows an embodiment where the capacitance CX or CY is coupled toa common power. Although all possible variations are not explicitlyshown in the Figures, the present technology covers all disclosedinstances of the clock circuit showing the capacitance CX or CY, wherethe clock circuit is modified to couple the capacitance CX or CY to acommon power.

In one embodiment, the capacitance CX or CY is actually a PMOStransistor with the opposite terminal decoupled from a common power withthe inverters.

The inverter circuitry 204A and 204B is driven by a source of CTATpower, or power that is conversely proportional to temperature, todecrease with increasing temperature.

The inverters are very different from the op amp version. In the op ampversion, a Vref is compared against the timing circuit output (e.g., RCcircuit rise/fall). But in the inverter version, the power of theinverter is controlled, to change the trip point of the inverter andthereby detect the timing circuit output (e.g., RC circuit rise/fall).In the inverter version, an additional temperature relationship betweenthe power and the trip point of the inverter is of concern.

The inverters are advantageous over the op amp version, for one or moreof the following reasons: (1) lower working VDD; (2) smaller circuitsize (inverter has only 2 MOSFETs, but the op amp has 5 or moreMOSFETs). (3) simpler design; (4) lower active current (inverter has onecurrent path, but the op amp has 2 or 3 current paths and includes anextra current mirror); and (5) higher speed (inverter has one stagedelay, the op amp has 2 or 3 stages of delay).

The latch circuitry 206 is cross-coupled, such that the output of onegate is coupled to the inputs of the other gate. One input of a gate isdirectly coupled to the output of another gate. Another input of a gateis directly coupled to the output of another gate through the timingcircuitry and the level detection circuitry.

FIG. 2C shows another embodiment of a clock circuit. Although otherwisesimilar to FIG. 2A, in FIG. 2C the parallel instances of invertercircuitry 204A and 204B are driven by sources of PTAT_power, or powerthat is proportional to temperature, to increase with increasingtemperature. Although all possible variations are not explicitly shownin the Figures, the present paper covers instances of the clock circuitshowing a source of CTAT_power, where the source of CTAT_power isreplaced with a source of PTAT_power.

Similarly, although all possible variations are not explicitly shown inthe Figures, the present paper covers all disclosed instances of theclock circuit showing a source of PTAT_power, where the source ofPTAT_power is replaced with a source of CTAT_power.

FIG. 2D is a diagram of an integrated clock circuit with tolerance totemperature variations, including Schmitt trigger circuitry to evaluatethe timing circuitry output.

Although similar to FIG. 2B, in FIG. 2D the level switching circuitry210A and 210B are instances of a Schmitt trigger driven by a source ofCTAT_power, and include op amps with closed loop positive feedbackthrough resistance.

FIG. 2E is a diagram of a Schmitt trigger circuit.

FIG. 3 is a circuit diagram of an integrated clock circuit withtolerance to temperature variations, including OP amp circuitry toperform level detection of the timing circuitry output by comparisonwith a reference.

Shown are parallel instances of timing circuitry 302A and 302B, parallelinstances of level switching circuitry 304A and 304B, and the latchcircuitry 306. The level switching circuitry 304A and 304B are OP ampcomparator with a reference voltage CTAT_REF. Otherwise, the clockcircuit is generally similar to FIG. 2A.

FIG. 4A is circuit diagram of the reference signal for the leveldetection circuitry, including a current source with current output thatincreases with increasing temperature.

FIG. 4A shows how the CTAT_power signal relied on by the level detectioncircuitry is generated, shown here as CTAT_REF 428. A constant currentsource PTAT_I 426, draws current that is proportional to temperature, toincrease with increasing temperature, from regulated power 422 throughresistor RES 424. The regulated power 422 supplies a constant voltageindependent of varying temperature. The regulated power supplies aconstant power and does not change with the VDD and temperature. Anexample is the output of a regulator with a bandgap reference. Theresulting output is conversely proportional to temperature, due to theincreasing voltage drop across the resistor with increasing temperatureand the placement of the output terminal on the lower side of thisvoltage drop. An example of the current source is shown in FIG. 4E.

FIG. 4B is a variation of the circuit of FIG. 4A, where the constantcurrent source PTAT_I 426 is replaced with the constant current sourceCTAT_I 430, and the CTAT_power signal CTAT_REF 428 relied on by thelevel detection circuitry is replaced with PTAT_power signal PTAT_REF432 relied on by the level detection circuitry. An example of: thecurrent source is shown in FIG. 4G.

FIG. 4C is a variation of the circuit of FIG. 4A, with a bypasscapacitor 434 in parallel with resistor RES 424, which decreases thenoise. Also, the current source includes a current mirror. An example ofthe current source circuit is shown in FIG. 4D.

FIG. 4D is a current generator based reference circuit providing PTATcurrent from PMOS devices.

FIG. 4E is a current generator based reference circuit providing PTATcurrent from NMOS devices.

In FIGS. 4D and 4E, the circuit uses the delta_Vgs between two MOStransistors having the same current, proportional to temperature. Sodelta_Vgs/resistance=PTAT_I. In FIGS. 4D and 4E, these two transistorsare identified with circles.

FIG. 4F is a current generator based reference circuit providing CTATcurrent from PMOS devices.

FIG. 4G is a current generator based reference circuit providing CTATcurrent from NMOS devices.

A current generator based reference circuit as described herein isadvantageous, because in several embodiments, a single kind oftemperature dependent parameter is controlled, instead of two kinds oftemperature dependent parameters associated with different materialshaving different temperature dependence.

FIG. 5A is circuit diagram of the reference signal for the leveldetection circuitry, including a current source with current output thatdecreases with increasing temperature.

FIG. 5A shows how the CTAT_power signal relied on by the level detectioncircuitry is generated, shown here as CTAT_REF 528. A constant currentsource CTAT_I 526, draws current that is conversely proportional totemperature, to decrease with increasing temperature, from regulatedpower 522 through resistor RES 524. The resulting output is converselyproportional to temperature, due to the decreasing voltage drop acrossthe resistor with increasing temperature and the placement of the outputterminal on the upper side of this voltage drop.

An example of the shown current sources is a cascade current source.

FIG. 5B, 5C, 5D, and 5E are other examples to generate the referencevoltage signal.

FIG. 5B is a variation of the circuit of FIG. 5A, where the constantcurrent source CTAT_I 526 is replaced with the constant current sourcePTAT_I 530, and the CTAT_power signal CTAT_REF 528 relied on by thelevel detection circuitry is replaced with PTAT_power signal PTAT_REF532 relied on by the level detection circuitry.

FIG. 5C is a variation of the circuit of FIG. 5A, where the resistor RES524 is replaced with the diode DI0 530. An example of the current sourceis shown in FIG. 4F.

FIG. 5D is a variation of the circuit of FIG. 5C, where the constantcurrent source CTAT_I 526 is replaced with the constant current sourcePTAT_I 530, and the placement of the output terminal is moved from theupper side of the voltage drop across the constant current source, tothe lower side of the voltage drop across the constant current source.

FIG. 5E is a variation of the circuit of FIG. 5C, where the constantcurrent source CTAT_I 526 is replaced with the resistor RES 524.

FIG. 6A is a set of graphs of time versus magnitude traces showing howclock circuitry that is intolerant of temperature variation generatesclock timing that varies widely with varying temperature.

FIG. 6A shows a range of traces at high temperature, low temperature,and intermediate temperature. The lower the temperature, the faster thetiming circuitry becomes, and the higher the temperature, the slower thetiming circuitry becomes. Due to the common timing circuitry reference,the timing circuitry reaches the reference more quickly at lowtemperature than at high temperature. Consequently, the timing of theclock circuitry is faster at low temperature than at high temperature.

FIG. 6B is a set of graphs of time versus magnitude traces showing howclock circuitry that is tolerant of temperature variation generatesclock timing is fairly constant with varying temperature, due tocircuitry such as that in FIGS. 2-5.

FIG. 6B shows a range of traces at high temperature, low temperature,and intermediate temperature. As in FIG. 6A, the lower the temperature,the faster the timing circuitry becomes, and the higher the temperature,the slower the timing circuitry becomes. However, different timingcircuitry references are used in FIG. 6B, in contrast with the commontiming circuitry reference used in FIG. 6A. Although the timingcircuitry reaches the reference more quickly at low temperature than athigh temperature, the timing circuitry reference is also correspondinglyhigher. Consequently, the timing of the clock circuitry shows littlevariation despite the temperature variation and resulting speedvariation in the timing circuitry.

FIGS. 7A and 7B are other embodiments, which show falling signals ratherthe rising signals of FIGS. 6A and 6B, but still show the same timeconstants.

Whether a clock signal relies on rising signals such as FIGS. 6A and 6B,or falling signals such as FIGS. 7A and 7B, depends on whether thecapacitance CX and CY is coupled towards ground as in FIG. 2A or towardspower as in FIG. 2B.

FIGS. 8A and 8B are circuit diagrams of an integrated clock circuit withtolerance to ground noise, including transistors that selectively couplethe ground noise as part of the reference signal used in level detectionof the timing circuitry output.

Shown are parallel instances of timing circuitry 802A and 802B, parallelinstances of level switching circuitry 804A and 804B, and the latchcircuitry 806. The level switching circuitry 804A and 804B selectivelycouples the ground noise coming from the level switching referencecircuitry 816A or 816B, and is stored in the capacitive node REF X orREFY, respectively subject to the switching action of the switchingtransistor 818A turned on by signal ENX and the switching transistor818B turned on by signal ENY. This acts as a sample and hold of groundnoise, so that the same ground noise is held by the timing circuitry802A or 802B, and by the level switching reference circuitry referencenodes REFX or REFY, relied on by the level switching circuitry 104.

In one embodiment, the capacitance CX or CY is actually a PMOStransistor with the opposite terminal decoupled from a common power withthe PMOS which connects to the RX or RY

OX is kept at ground when ENX is high. Then ENX goes low and turns offthe NMOS; at this moment the ground noise is held in the OX. If thenoise is high then the pre-charge speed is fast; if the noise is lowthen the pre-charge speed is slow. This circuit lets the REFX or REFYhold the same ground noise at the same time.

In FIG. 8A the switching reference circuitry reference nodes REFX orREFY, includes capacitance circuitry coupled towards ground. In FIG. 8Bthe switching reference circuitry reference nodes REFX or REFY, includescapacitance circuitry coupled towards power.

In various embodiments, the level switching reference circuitry 816A or816B are two sets of circuitry, or the same set of circuitry shared bythe multiple parallel instances of timing circuitry and the multiplelevel switching circuitry 804A and 804B.

FIG. 9 is a set of graphs of voltage versus time, showing how clockcircuitry that is intolerant of ground noise, will generate clock timingthat varies widely with time-varying ground noise.

FIG. 9 shows how traces OX and OY are affected by ground noise, in thiscase the REF_LO signal. When there is a peak in ground noise, then theprocess of the timing circuit charging from REF_LO to REF_HI gets a headstart, resulting in less time being required for the timing circuit tocharge from REF_LO to REF_HI. Accordingly, the resulting clock signaloutput 910 has a wide variation in clock period.

When ENX goes high, the OX is kept at ground and the voltage varies withthe ground noise. When ENX goes low, and turns off the NMOS, then theground noise is kept at the OX. But the reference level still varieswith the ground noise without more. The worse case is that OX holds ahigh ground noise and during the charging period the reference circuitsuffer a negative ground level; then the reference is much lower thanexpected. So a sample and hold like structure keeps the same groundnoise in the REFX or REFY.

FIG. 10 is a set of graphs of voltage versus time, showing how clockcircuitry that is tolerant of ground noise, will generate clock timingthat is fairly constant with time-varying ground noise, due to circuitrysuch as that in FIG. 8.

FIG. 10 shows how traces OX and OY are affected by ground noise, in thiscase the REF_LO signal. When there is a peak or other variation inground noise, this peak or other variation is stored in the respectivecapacitor for REFX or REFY of FIG. 8. Because ground noise affectingREF_LO is tracked by this sample-and-hold reference circuitry, the leveldetection circuitry compares the same ground noise from the leveldetection reference circuitry, and the timing circuitry. After theground noise is sampled and held in this manner, the ground noise, whichcontinued to change, is decoupled from the sampling circuitry.Accordingly, in the process of the timing circuit charging from REF_LOto REF_HI, there is no “head start”, and the same time is required forthe timing circuit to charge from REF_LO to REF_HI, despite the groundnoise. Accordingly, the resulting clock signal output 910 has a commonclock period during a wide variation in ground noise.

Another embodiment is directed to sampling the ground noise and thendecoupling the ground noise from the sampling circuitry duringdischarging, rather than decoupling the ground noise from the samplingcircuitry during charging as in FIGS. 9 and 10. This embodiment carriesthe additional difficulty of having to address power noise from thenoise regulator power.

In another embodiment (like FIG. 2C), the sample and hold circuit willhold the power noise instead of the ground noise.

FIGS. 11A and 11B are circuit diagrams of an integrated clock circuitwith tolerance to power noise, including transistors that share a commonnoise phase of power noise in the timing circuitry power, and powernoise in the reference signal used in level detection of the timingcircuitry output.

Shown are parallel instances of timing circuitry 1102A and 1102B,parallel instances of level switching circuitry 1104A and 1104B, and thelatch circuitry 1106. Also shown are parallel instances of timing powerand level switching generator 1116A and 1116B, which generate powernoise with the same noise phase in both the power noise in the timingcircuitry power, and the power noise in the reference signal used inlevel detection of the timing circuitry output.

In FIG. 11A the capacitance circuitry CX or CY is coupled towardsground. In FIG. 11B the capacitance circuitry CX or CY is coupledtowards power 1116A or 1116B.

FIG. 12 is a circuit diagram of the power circuitry that shares thecommon noise phase of power noise in the timing circuitry power, andpower noise in the reference signal used in level detection of thetiming circuitry output.

FIG. 12 shows a power source 1236, driving an op amp 1232. The op amphas a reference signal REF_OP 1234 in the noninverting input. An exampleof REF_OP 1234 is a bandgap reference circuit at 1.3 V. A MOFET 1238 hasa gate coupled to the output of op amp 1232, a drain coupled to thepower source 1236, and a source coupled to the timing power output 1246.The timing power output 1246 is separated by resistor R1 1240 from thelevel switching reference 1248. Resistor R2 1242 separates the levelswitching reference 1248 from the negative feedback point of the op amp1232. Finally, resistor R3 couples this feedback point to ground.

Another embodiment employs capacitive coupling with a floating node tomaintain the same noise phase between the timing power output 1246 andthe level switching reference 1248, where one of the timing power output1246 and the level switching reference 1248 is floating.

Although the above embodiments are specifically designed to maintain thesame noise phase between the timing power output 1246 and the levelswitching reference 1248, this is not the case in other designs. Suchother designs have different noise phase between the timing power outputand the level switching reference 1248, for one or more various reasons:(1) the reference circuit is not near the timing circuit due to the chipplan; (2) the reference circuit is a regulator which has better PSRR(power supply rejection ratio) than VDD power; and (3) even with a powerregulator for the RC power, a noise phase difference remains, due to thedifferent output loading and transient, and the power regulator havingto support larger current and larger output transient.

FIG. 13 is a set of graphs of voltage versus time, showing how powernoise has the same phase in both the timing circuitry power, and thereference signal used in level detection of the timing circuitry output,due to circuitry such as in FIGS. 11 and 12.

The same noise phase is shown in both the power noise in the timingcircuitry power 1301, and the power noise in the reference signal usedin level detection of the timing circuitry output 1302. Trace 1303overlaying traces 1301 and 1302 show that, although the magnitudes ofthe power noise vary, the peaks and valleys are synchronous in the powernoise between traces 1301 and 1302.

FIG. 14 is a set of graphs of voltage versus time, showing how clockcircuitry that is intolerant of power noise, will generate clock timingthat varies widely with time-varying power noise.

FIG. 14 shows how traces OX and OY are affected by power noise 1401.When there is a dip in power noise, then the process of the timingcircuit charging from REF_LO to REF_HI gets a head start, resulting inless time being required for the timing circuit to charge from REF_LO toREF_HI. Similarly, when there is a peak in power noise, then the processof the timing circuit charging from REF_LO to REF_HI gets slowed,resulting in more time being required for the timing circuit to chargefrom REF_LO to REF_HI. These variations follow from the constant levelswitching reference. Accordingly, the resulting clock signal output 1410has a wide variation in clock period.

FIG. 15 is a set of graphs of voltage versus time, showing how clockcircuitry that is tolerant of power noise, will generate clock timingthat is fairly constant with time-varying power noise, due to circuitrysuch as that in FIGS. 11 and 12.

FIG. 15 shows how traces OX and OY are affected by ground noise. Unlikein FIG. 14, when there is a peak or other variation in power noise 1501,there is a synchronous has peak or other variation in the levelswitching reference. Although the magnitude of these peaks or othervariations are lessened in the level switching reference, as compared tothat of the power noise, the synchronous nature of the power noisebetween the timing circuitry power 1501 and the level switchingreference substantially decreases the clock signal variation.Accordingly, the resulting clock signal output 1510 has a common clockperiod during a wide variation in ground noise.

FIGS. 16A and 16B are circuit diagrams of an integrated clock circuit toswitch the power of the clock. During power on, the stable power isn'tready, and needs the VDD power to generate the clock for the logiccircuits. Logic circuitry waits for the stable power setup timing. Whenthe stable power is ready, then the clock will switch to a stable clock.

Shown are parallel instances of timing circuitry 1602A and 1602B,parallel instances of level switching circuitry 1604A and 1604B, and thelatch circuitry 1606. Also shown are parallel instances of timing powerand level switching generator 1616A and 1616B, which generate powernoise with the same noise phase in both the power noise in the timingcircuitry power, and the power noise in the reference signal used inlevel detection of the timing circuitry output. Also shown are switches1620A between the VDD and the timing power and level switching generator1616A, switches 1620B between the VDD and the timing power and levelswitching generator 1616B, switches 1620C between different types oflevel switching circuitry 1604A and the latch 1606, and switches 1620Dbetween different types of level switching circuitry 1604B and the latch1606.

In FIG. 16A the capacitance circuitry CX or CY is coupled towardsground. In FIG. 16B the capacitance circuitry CX or CY is coupledtowards power 1616A or 1616B.

FIG. 17 is block diagram of a memory circuit with an improved integratedclock circuit as discussed herein.

FIG. 17 is a simplified block diagram of an integrated circuit 1700including a memory array 1712. A word line (or row) and block selectdecoder 1714 is coupled to, and in electrical communication with, aplurality 1716 of word lines and string select lines, and arranged alongrows in the memory array 1712. A bit line (column) decoder and drivers1718 are coupled to and in electrical communication with a plurality ofbit lines 1720 arranged along columns in the memory array 1712 forreading data from, and writing data to, the memory cells in the memoryarray 1712. Addresses are supplied on bus 1722 to the word line decoderand drivers 1714 and to the bit line decoder 1718. Sense amplifiers anddata-in structures in block 1724, including current sources for theread, program and erase modes, are coupled to the bit line decoder 1718via the bus 1726. Data is supplied via the data-in line 1728 frominput/output ports on the integrated circuit 1710, to the data-instructures in block 1724. In the illustrated embodiment, other circuitry1730 is included on the integrated circuit 1700, such as a generalpurpose processor or special purpose application circuitry, or acombination of modules providing system-on-a-chip functionalitysupported by the memory cell array. Data is supplied via the data-outline 1732 from the sense amplifiers in block 1724 to input/output portson the integrated circuit 1700, or to other data destinations internalor external to the integrated circuit 1700. State machine and improvedclock circuitry (as discussed herein) are in circuitry 1734.

FIG. 18 is a circuit diagram, similar to FIG. 16, of an integrated clockcircuit with tolerance to power noise, and further including switchingcircuitry between the reference generator and the op amp. As in FIG. 8,the switching transistor 818A is turned on by signal ENX and theswitching transistor 818B is turned on by signal ENY. Similar to FIG. 8,ground noise coming from the timing power and level switching generator1616A and 1616B is stored in the capacitive node REF X or REFY.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than in a limitingsense. It is contemplated that modifications and combinations willreadily occur to those skilled in the art, which modifications andcombinations will be within the spirit of the invention and the scope ofthe following claims.

1. An apparatus, comprising: a clock integrated circuit, comprising: atiming circuit having an output alternating between a first referencesignal and a second reference signal at a rate determined by a timeconstant determining timing of a clock signal output of the clockintegrated circuit, the second reference signal including a varyingnoise signal; clock power and reference circuitry having the varyingnoise signal, the clock power and reference circuitry generating thesecond reference signal with a first version of the varying noisesignal, the clock power and reference circuitry generating a levelswitching reference signal with a second version of the varying noisesignal, the first version of the varying noise signal synchronized withthe second version of the varying noise signal, such that variations inthe first version of the varying noise signal are synchronized withvariations in the second version of the varying noise signal; and alevel switching circuit comparing an output of the timing circuit withthe level switching circuit reference signal, an output of the levelswitching circuit determining the clock signal output of the clockintegrated circuit.
 2. The apparatus of claim 1, wherein the varyingnoise signal is a varying power noise.
 3. The apparatus of claim 1,wherein the variations in the first version of the varying noise signalhave different magnitudes from the variations in the second version ofthe varying noise signal.
 4. The apparatus of claim 1, wherein the clockpower and reference circuitry has a first output for the secondreference signal, and a second output for the level switching referencesignal, and the varying noise signal is synchronized across the firstoutput and the second output via a resistance coupled between the firstoutput and the second output.
 5. The apparatus of claim 1, wherein theclock power and reference circuitry has a first output for the secondreference signal, and a second output for the level switching referencesignal, and the varying noise signal is synchronized across the firstoutput and the second output via a capacitance coupled between the firstoutput and the second output.
 6. The apparatus of claim 1, wherein theclock power and reference circuitry has a first output for the secondreference signal, and a second output for the level switching referencesignal, and the varying noise signal is synchronized across the firstoutput and the second output via a capacitance coupled between the firstoutput and the second output, and one of the first output and the secondoutput is floating.
 7. The apparatus of claim 1, further comprising: aplurality of switches decoupling the level switching circuit duringpower on.
 8. The apparatus of claim 1, wherein the first referencesignal is a first reference voltage, the second reference-signal is asecond reference voltage, and the timing circuit alternates betweencharging from the first reference voltage to the second referencevoltage and discharging from the second reference voltage to the firstreference voltage.
 9. The apparatus of claim 1, wherein the timeconstant characterizes an exponential signal.
 10. The apparatus of claim1, the clock integrated circuit further comprising: a latch circuitgenerating the clock signal output of the clock integrated circuit,responsive to the output of the level switching circuit.
 11. Theapparatus of claim 1, the clock integrated circuit further comprising: alevel switching reference circuit generating the level switchingreference signal, including: an output generating the level switchingreference signal; a PTAT (proportional to temperature) current generatorgenerating current flowing by the output; and a resistance adjacent tothe output.
 12. The apparatus of claim 1, the clock integrated circuitfurther comprising: a level switching reference circuit generating thelevel switching reference signal, including: an output generating thelevel switching reference signal; a CTAT (conversely proportional totemperature) current generator generating current flowing by the output;and a resistance adjacent to the output.
 13. The apparatus of claim 1,the clock integrated circuit further comprising: a level switchingreference circuit generating the level switching reference signal,including: an output generating the level switching reference signal; aPTAT (proportional to temperature) current generator generating currentflowing by the output; and a parallel capacitance and resistanceadjacent to the output.
 14. The apparatus of claim 1, the clockintegrated circuit further comprising: a level switching referencecircuit generating the level switching reference signal, including: anoutput generating the level switching reference signal; a CTAT(conversely proportional to temperature) current generator generatingcurrent flowing by the output; and a parallel capacitance and resistanceadjacent to the output.
 15. A method, comprising: determining timing ofa clock integrated circuit by alternating a timing circuit outputbetween a first reference signal and a second reference signal at a ratedetermined by a time constant determining the timing of the clockintegrated circuit; generating the second reference signal with a firstversion of a varying noise signal and a level switching reference signalwith a second version of the varying noise signal, the first version ofthe varying noise signal synchronized with the second version of thevarying noise signal, such that variations in the first version of thevarying noise signal are synchronized with variations in the secondversion of the varying noise signal; and comparing the timing circuitoutput with the level switching reference signal, to determine a clocksignal output of the clock integrated circuit.
 16. The method of claim15, wherein the varying noise signal is a varying power noise.
 17. Themethod of claim 15, wherein the variations in the first version of thevarying noise signal have different magnitudes from the variations inthe second version of the varying noise signal.
 18. The method of claim15, wherein said generating includes: synchronizing the first versionand the second version of the varying noise signal by coupling thesecond reference signal and the level switching reference signal with aresistance.
 19. The method of claim 15, wherein said generatingincludes: synchronizing the first version and the second version of thevarying noise signal by coupling the second reference signal and thelevel switching reference signal with a capacitance.
 20. The method ofclaim 15, wherein said generating includes: synchronizing the firstversion and the second version of the varying noise signal by floatingone of the second reference signal and the level switching referencesignal, and coupling the second reference signal and the level switchingreference signal with a capacitance.
 21. The method of claim 15, furthercomprising: decoupling the synchronized versions of the varying noisesignal during power on, such that said determining and said comparing donot rely on the synchronized versions of the varying noise signal duringpower on.
 22. The method of claim 15, wherein the first reference signalis a first reference voltage, the second reference signal is a secondreference voltage, and the timing circuit alternates between chargingfrom the first reference voltage to the second reference voltage anddischarging from the second reference voltage to the first referencevoltage.
 23. The method of claim 15, wherein the time constantcharacterizes an exponential signal.
 24. The method of claim 15, furthercomprising: after said comparing, generating the clock signal output ofthe clock integrated circuit with a latch circuit.
 25. A method ofmanufacturing an apparatus, comprising: providing a clock integratedcircuit, comprising: providing a timing circuit having an outputalternating between a first reference signal and a second referencesignal at a rate determined by a time constant determining timing of aclock signal output of the clock integrated circuit, the secondreference signal including a varying noise signal; providing clock powerand reference circuitry having the varying noise signal, the clock powerand reference circuitry generating the second reference signal with afirst version of the varying noise signal, the clock power and referencecircuitry generating a level switching reference signal with a secondversion of the varying noise signal, the first version of the varyingnoise signal synchronized with the second version of the varying noisesignal, such that variations in the first version of the varying noisesignal are synchronized with variations in the second version of thevarying noise signal; and providing a level switching circuit comparingan output of the timing circuit with the level switching circuitreference signal, an output of the level switching circuit determiningthe clock signal output of the clock integrated circuit.